What special dietary instructions should I follow? Do not stop taking sildenafil without talking to your doctor. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. Sildenafil may cause side effects.Compare prices and print coupons for Viagra (Sildenafil) and other drugs at CVS, Walgreens, and other pharmacies. Prices start at $ Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects . You’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity. Based on how well you respond to this .